1. Field of the Invention
The present invention is concerned with methods for inhibiting and decreasing cell motility (and particularly that of melanoma cells) by contacting such cells with relatively minor amounts of metal ion(s) selected from the group consisting of cobalt ion, the lanthanide metal ions, and mixtures thereof. In practice, metal ion sources (e.g., the metal halide salts) are solubilized in an aqueous medium and are administered to melanoma cells to achieve motility inhibition.
2. Description of the Prior Art
Metastasis, the spread of cancerous cells from an initial tumor to other physically separate sites in the body, is a common and life-threatening situation in many cancers. Although the precise mechanism of metastasis is not known, directional migration of melanoma cells in response to concentration gradients of soluble factors (chemotaxis) and overall motility of melanoma cells is clearly an important factor.
Savarese et al., Type IV Collagen Stimulates and Increase in Intracellular Calcium; Potential Role in Tumor Cell Motility; J Biol. Chem., 267(30):21928-21935 (1992) examined the influence of two metal ions (Co2+ and La3+) on motility of A2058 human melanoma cells. The concentration of Co2+ used in this study (10xe2x88x928 to 10xe2x88x924 M) was completely ineffective to inhibit tumor cell motility. Indeed, only one of six agents (nifedipine) at a concentration of 100 xcexcM was reported to produce inhibition of motility.
Co2+ is widely known and used for its effects in blocking Ca2+ currents in a variety of cell systems. The concentration of Co2+ utilized is based on 1979 experiments in which CoCl2 was used to block neuromuscular transmission. Gd3+ is also known as a highly potent channel blocking agent for stretch-sensitive non-selective cation channels, and may be more selective for this channel type as compared with voltage-gated Ca2+ channels. For example, a recent study indicates that Gd3+ (up to 100 xcexcM), in contrast to Co2+ has no effect on the voltage-gated channels that control quantal neurotransmitter release at the mammalian neuromuscular junction (Porter et al., Br. J Pharmacol., 118:27-32 (1996)). Additional reports indicate an effect of Gd3+ on voltage-gated Ca2+ channels in isolated guinea pig ventricular myocytes (Lacampagne et al.; Biochem. Biophys. Acta., 1191:205-208 (1994)) and cultured pituitary cells (Biagi et al., Amer. J. Physiol., 259:C515-C520 (1990)). At present, the primary medical use for gadolinium involves chelated forms of the element used as contrast agents in magnetic resonance imaging. However, there are no previous reports on the use of gadolinium ion for decreasing melanoma cell motility.
U.S. Pat. No. 4,690,935 deals with selective blockers of voltage-gated Ca2+ channels in tumor cell metastasis. U.S. Pat. No. 5,045,543 describes 5-amino or substituted amino 1,2,3-triazoles as being effective against progressive metastatic cancers (Kohn et al, Cancer Res., 56:569-573 (1996)). These patents do not disclose the utility of cobalt or the lanthanide metal ions for inhibiting melanoma cell motility.
The present invention describes a novel method for inhibiting cell motility comprising the step of contacting a cell with a motility-inhibiting amount of a metal ion selected from the group consisting of cobalt ion, the lanthanide metal ions (La, Ce, Pr, Nd, Pb, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu). Through use of the present invention, a decrease in motility of at least about 50%, and more preferably from about 70-95%, can be obtained, as compared with the motility of the cell under identical conditions, but in the absence of the metal ion contacting step.
In more detail, the contacting step is preferably carried out by administering a metal ion source for cell contact by dispersing the metal ion source in an aqueous saline system having a motility-inhibiting metal ion concentration of from about 20 xcexcM to about 2 mM. The preferred metal ion sources are the corresponding metal salts, and particularly the halogen salts such as the chloride salts.
The most preferred metal ions for use in the invention are selected from the group consisting of cobalt and gadolinium ions and mixtures thereof. Where gadolinium ion is employed, the ion concentration of the liquid system used for motility inhibition should be from about 1-200 xcexcM, preferably from about 10-100 xcexcM, more preferably from about 20-50 xcexcM, and even more preferably about 20 xcexcM. Correspondingly, where cobalt ion is employed, the ion concentration of the liquid system is most preferably about 2 mM.
The contacting step of the invention may be carried out in vitro and in such instances the cell is dispersed in a liquid saline cell-supporting medium, and selected motility-inhibiting metal ions are added to the medium to achieve the desired ion concentration. Preferably, the medium should be maintained at a temperature of from about 30-44xc2x0 C. and the contacting step is carried out under a CO2-enriched atmosphere (e.g., 5% by volume CO2). In such instances, additional cell motility inhibition can be obtained by adjusting the potassium ion concentration of the cell-supporting liquid medium, preferably to a level of below about 0.5 mM or above about 30 mM. The invention can also be carried out in vivo by administration of metal ion (typically a halogen salt thereof dispersed in a liquid saline carrier) to a mammalian subject at or near the site of a potentially metastatic tumor.